Fluid coking with cracking of more refractory oil in the transfer line



Dec. 22, 1964 C, L, PERSYN 3,162,593

FLUID COKING WITH CRACKING OF MORE REFRACTORY OIL IN THE TRANSFER LINE IFiled March 2l, 1962 A TTORNEV United States Patent O 3,l62,53 FLUED CmlWH'H CRASEQNG Gli MORE REFRAQTSRY GEL EN @H- ERANSFER LNE Charles L.Persyn, Concord, Calif., aasignor to Tidewater @il Company, Los Angeles,Calif., a corporation of Delaware Filed Mar. 21, 1962, Ser. No. lSlAil 4Claims. (Cl. L20S- 53) This invention relates to an improved petroleumrelining process involving improvements in iiuid coking for upgrading ofheavy oils. More specific aspects of the invention relate to novelrelationships between catalytic cracking and iluid coking.

As is well known in the art, the duid coking process uses a fluidcolting vessel or reactor and an external heating vessel, eg., a uid bedburner. A fluid hed of solids, preferably coke particles produced by theprocess having a size in the range of about 40 to 1000 microns, ismaintained in the Cokin(T zone by the upward passage of a iiuidizinggas, usualiy steam. The temperature of the bed is maintained at about950 F. by circula.'ng solids (coke) to the heating vessel (coke burner)and back. The heavy mineral oil to be converted is injected into theiluid bed and upon Contact with the hot solids undergoes pyrolysisevolving lighter hydrocarbon vapors and depositing coke on the solids.The turbulence of the iiuid bed normally results in substantiallyisothermal conditions and in thorough and rapid distribution of theheavy injected oil. `Product vapors, alter heavy entrained solids areremoved, are withdrawn overhead from the coking vessel and sent to ascrubber and fractionator for cooling and separation. Generally, astream of the coke particles is continuously withdrawn from the cokingvessel or reactor and passed to the burner, where some of its is burnedto heat the remainder, and heated coke is continuously recirculated tothe reactor.

ln the scrubber the heavier constituents of the effluent product vaporare condensed, usually with the aid of a quench oil, which may be atleast a portion of the heavy oil fed to the coking reactor, in order toremove any coke particles and other undesirable heavy elements intheform or a slurry, this slurry being then fed to the coiring reactor forfurther treatment. From the top of the scrubber, the cracked vapors passto the ractionator, where they are separated into gas, gasoline, and alight gas oil. The Light gas oil is normally used as charge stock forcatalytic cracking o any of several types, including the more recenthydrocracking.

From a point near the top of the scrubber there is also Withdrawn astream of heavy gas oil, which, by reason of its nitrogen content, ashcontent, or aromaticit is decidedly unsuitable as a catalytic crackingfeed stock because it fouls the catalyst. Heretoiore, this heavy gas oilhas been used principal-ly as an element of fuel oil. However, fueloilis not nearly such a profitable product as gasoline; so attempts havebeen made to'recycle this l it could be reduced completely tolighterdistillates. As conversion of this material must ta1 e place inthefvapor phase because its boiling range islovver than that of theheavy feedstock, such recycle operation is not attractive. Because vtheCoking temperature in the coking reactor is relatively low, highconversion of the refractory heavy gas oil is dilicult to obtain andapparently less than 5% heavy gas oil through the coking reactor in thehope that ih/ii Patented Dec. 22, 3.9%@

ice

of it is converted by such recycle. This results, then, in excessiverecycle rates. This diiiiculty cannot economically be circumvented byincreasing the coking temperature in the coking reactor, because such anincrease would resuit in excessive thermal degradation and loss of thelight distillate products.

it has also been suggested that this heavy gas oil be cracked at veryhigh temperatures (e.g., 12G0 F. to 1600" F.) to produce gases, but thisrequires separate reactors and results in products that generally areless valuable than gasoline and catalytic cracking charge stock.

have found, however, that by introducing the heavyV gas oil into thetransfer stream of coke coming from the coke burner to the cokingreactor, in which stream the temperature is higher than in the reactorbed, being in the neighborhood of ll0O to l150 F., a considerable amountof the heavy gas oil can be converted to gasoline, light gas oilsuitable for catalytic cracking, and etiluent gases, while certain otherportions take on characteristics like that of the oill in the recycleslurry, so that further recycle, possibly until extinction, becomesfeasible.

Another petroleum process which has achieved great importance is that ofcatalytic cracking, including the more recently developed hydrocracking.Catalytic cracking units require a charge stock muchhigher in grade thanthat of iiuid coking units. In fact, iiuid coking units are customarilyaddedl to reiineries for the purpose of handling residuum which would becertain toy foul catalytic cracking units and which would give very poorresults in other types of cracking units. As already mentioned, thelight gas oil produced by a uid coking unit is good charge stock for thecatalytic cracking unit, and it is produced in even greater quantity bythe use of-the present invention. Other suitable charge stocks come fromother portions of the refinery.

In the catalytic cracking unit most of the charge stock is upgraded togasoline and other high grade products. The remainder, a heavy fractioncontaining (in a duidized catalytic cracking process) entrainedcatalyst, is settled out and a clarified portion is decanted oli. Thisportion, known as decanted oil, is fairly low-grade stock, whichheretofore has been used mainly as fuel oil. It has many of thecharacteristics of coker heavy gas oil and the effects of adding it to afluid coker are similar to those obtained from adding heavy Coker gasoil.

I have found that decanted oil from a iiuid catalytic cracking unit canalso he upgraded by charging it to the hot coke line.

Thus, the invention links iiuid coking and iiuid catalytic cracking in anew wayand accomplishes a novel type of recycle and cracking for boththe decanted oil from the catalytic cracking unit andy the heavy gas Oilobtained from the Coker unit.

Other objects and' advantages of therinvention will appear from thefollowing description of a preferred ernbodiment thereof.

The drawing is a diagrammatic representation of processing stepsincorporating the principlesof the present invention, and illustratesdiagrammatically yboth a fluid catalytic oracle-lng unit and auidcokingunit operating in conjunction with eachother. For purposes ofsirnplicity, most of the steam inlets, pumps, blowers, coolers, andsimilar details well known to the art have been omitted.

The drawing illustrates a lluid coking reactor 1 and aisaeas a cokeburner 2. In the coke burner 2 coke is burned to provide heat for thecokingreactor 1 and hot coke is returned to the coking reactor 1`through a hot line 3,

preferably and normally entering the upper part of reactor 1 asindicated in the drawing. To the colting reactor 1, which is at atemperature of between 925 and 1000 F., a charge stock of Vresiduum andrecycled slurry enters below the hot coke (see the drawing) from lines 4and 5 via a suitable manifold system. The injected oil contacts a bed 6of iluidized cokel and undergoes pyrolysis, evolving lighter hydrocarbonvapors and depositing additional coke on the coke particles.

Fluidization gas, eg., steam, is injected at numerous points, indicatedin the drawing by lines 7 and 8, to maintain uidization of the cokeparticles and to eect transfer of coke from the burner Z to thereactor 1. Coke particles, after having been stripped of entrainedhydrocarbons and after having oversize particles screened out andremoved through a line' 9, are withdrawn from the base ofthe vessel 1and sent to the coke burner 2 through line 10, to which steam or air issupplied as by a line 11.

Coke in excess of Vthat neededrfor burning andrecirculation to thereactor 1, where it supplies heat for the exothermic coking reaction, iswithdrawn from the burner 2 y through a line 12. v

From the reactor 1, the vaporous conversion products are withdrawnoverhead through cyclone separators 13 which remove fine particles ofentrained coke and return the fresh feed may be fed as quenchoil througha line 15 and from which a slurry is withdrawnthrough aline y 16 forrecycle either to the Vquench line 15 (after settling in a settler 17and cooling in a heat exchanger19) or to the recycle line 5 or both.From the scrubber 14, the uncondensed eiiluent passes overhead through aline 18 to a fractionator unit 20 where various fractions are taken off,such as gases and gasoline vapor'in line 21, a light gas oil (boilingbelow 630 F.) in line 22, land a heavy portion that is recycled as reuxbyline 2.3. Near thetop of the scrubber 14, heavy gas oil (mostlyboiling in the 600-900 F. range) is withdrawn by a line 24.

Heretofore, the heavy gas oil withdrawn through the line 24 has beenpassed to storage (represented by a tank 25') for disposal as fuel oil.in the present invention valves 26 and 27 `may be linstalled in the line24 and part or `all of the heavy gas oil may be ysent through the valve27 and a line 28 into the hot coke riser line 3 at a point 30 where thecoke is about ll00 'tol l150 F. The oil entering theV line 3 at thepoint 30 vaporizes almost instantly and acts as a fluidizing vaporsothat much less, if any, steam need be added-through the line 8 orY Yelsewherefin the liney 3 in order to impart proper movement to the cokefluidized in the line 3. 'While passing with this very hot coke throughthe'line 3 into the reactor 1, this heavy gas oil-Which cannot `becracked bycontact with the coke in the reactor 1iscracked to yieldadditional light gas oil, gasoline, gases, and a residue lof Y heaviergas oil, much of -Which becomes part of the re-V I cycle slurryV and maybe-capaole of cracking when recycled with it. Po,ssibly,'the veryvolatility of the heavyV gas oilcombines with itsrefractoriness toprevent'crack- Y ing when it isfed to the coking reactor bed bylessening kthe dwell timeitherei surely there is Vno such effecten dwellj Y time when itis fed to the line 3, since it has to; pass -j` throughthat Vline.A` At any-rate, the desired cracking of,Y

a substantial partis attained by thisinvention. Another part Vgoes intothe; heavy gasoil lineZ- again'for Va re- Y cycle to thelirieifror totheffuel oilstorage unit 25. f 'Y As illustratedin lthe drawing, the;lightVV gas oil V,withdrawn through the line 22 isV charged via lines3,1 andv 32 to a` fluidized catalyticy crackn'gfreactor 33 along with,other catalytic cracker charge stock. Catalyst fromV a regenerator 34is fed inV a fluidi'zed conditionthrough the line'v32'gto thereactor,and isfreturned through line' Y35 from the reactor 33 to the regenerator34. The eiluent fromrthe reactor 33 passes through a line 36 to afractionator 37, whence gas and gasoline are taken oif through a line33light gas oil through line 39, and heavy cat- 5 alytic gas oil throughline 40 (having quite different properties from the heavy coker gas oilin line 24). A bottoms fraction'containing catalyst fines which wereentrained in the vapors in the line 36 is passed by a line 41 to a DorrYclarifier 42;,whence a decanted oil is withdrawn through a line 43.This decanted'oil (having a boiling range substantially; between 600 and900 F.) Y has heretofore been sent to fuel oil such as to the storagetank 2'5 through line 45. According to a specific embodiment of thisinvention, ka portion at least of this decanted oil is diverted byyvalves 46 and 47 into the line 28 andl is` charged into the hot cokeline 3, where it is cracked in a reaction similar to that of the heavygas oil which it resembles in manyways.V If desired, the two may becharged as a mixture.

v Turning now vto a specific example, a residuum feed stock coming intothe coking'unit 1 through the charge line 4 may be as follows:

Y TABLE I 20 Properties of Feed Stock Residuum Charged to the l CokingReactor API gravity 8.0 30 Conradson carbon, wt. percent 14.3 Surfur,wt. percent 2.7 A.S.T.M. distillation (i3-1160), F.: TBP 614 Y 10% 89133% 1000 The conditions in thercoking reactor 1 are shown in Table yII.yY Y TABLE II Operating ConditionsV in Cokz'ng Reactor Pressure, p,.s.i.gFeed inlet temperature, F. 620 Reactor temperatures, F.: 5 Dense phase970 `Dilutephase 1015 lBurner temperature, F. 1150 Vapor holding time,total seconds 18 VCokein reactor, tons 800 5a'Coke circulation,tons/minute 45 to 55 The heavy gas oil eiuent (line 24) has thefollowing properties: f

Y TABLE III as f Properties o'f the Heavy Gas Oil Eiuenl Gravity, API,10.7 Y Conradson carbon, wt.vpercent' 0.83 50 Pourpoint, 'F.1 Y 70Sulfur, percent 1.77 'Nitrogen wt. percent 0.97

Viscosity: 1 f 5 I s v, sSFatizzfrF. f 3s` Y @5 SSUar210?F.i Y Y 55.6y

` YMetals,p'.p.m.:fY 1- Y' v Vanadium 0.014V

` Nickel-f Distillation, F., (distilled at For the purpose of comparisonin this example, this heavy gas oil is divided into three samples, and,at separate times, each sample is separately charged to the cokingsystem. Sample 1 is processed in the reactor 1, and Samples 2 and 3 areprocessed in the line 3, all under the conditions given in Table IV,where the Samples 1, 2, and 3 are compared with a Sample 0 representingthe conventional processing in which the heavy gas oil is not recycledat all.

TABLE IV Fluid Coking of Heavy Gas Oil of Table III, Operating DataSample No 0 1 2 3 Fresh Feed Rate, b./d 42, 000 42, 000 42, 000 42, 000Recycle Rate, Vol. Percent of Fresh Feed 40. 0 40. 0 40. 0 40, 0 HeavyCoker Gas Oil:

To Hot Coke Riser Line, b.ld 0 0 5,000 5, 000 To Coker Reactor, bJd 0 5,000 0 0 Recycle Rate, Considering Heavy Coker Gas Gil as Recycle, Vol.Porcent of Fresh Feed 40.0 51. 9 51.9 51.9 Reactor Holdup, Tons ofCoke.. 800 S00 800 800 Reactor Temperature, Bed, o F 070 970 970 970Reactor Temperature, Vapor Phase,

F 1, 015 1,015 1,015 1,015 Reactor' Pressure, p.s. 1 12 12 12 BurnerTemperature, 1, 150 1, 160 1, 130 Temperature at Hot Coke Riser Line l1,150 1,150 1,150 1, 100 Coke Burned, Tons/Day 520 520 520 520 Steam toHot Coke Transfer Line,

lhs/hr 49,000 50,000 32, 000 30,000

The coke circulation rate is in all four cases between 45 and 55 tonsper minute, the addition of up to 5000 b./d. of heavy gas oil apparentlynot requiring a material increase in burner temperature or circulationrate of coke.

The yields of these three samples are as follows:

TABLE V Samples Normal Operttion 1 2 3 Dry gas (C: Minus) M i 3.0.1.!(127, 090 i 2T, 790 34, 390 3l, 02o Total Propanes, b /d 2, 814 2, 854 3,824 3, 354 Total Butanes. b./d l, 974 1, 999 2, 444 2, 269 Gasoline (390F. ot 90% Dist.) b./d l2, 222 12, 372 l2, 892 13, 002 Light Gas Oil (600F. at l 90% Dist), b./d 4,578 l 4,738 4,703 4,983 Heavy Gas Oil (030 F.

plus), b./d 13, 692 1 13, 282 l 10, 420 1 1l, 207 Coke, gross, M ibs/da, e46 3, @so 3, ses 3, cs2

1 Net after deducting the 5,000 b./d. heavy gas oil recharged.

From Table V it will be seen that straight recycling of heavy gas oil tothe coking reactor (Sample 1) accomplishes little, while theintroduction of the heavy gas oil into the hot coke riser in accordancewith the invention (Samples 2 and 3) produces good yields of desirableproducts.

It will be noted especially that gasoline and light gas oil, suitablefor catalytic cracking charge, are increased a substantial amount by theinvention and that the heavy gas oil has been substantially reduced.

it is also to be noted that a transfer line temperature of 1100 F.affords substantially better yields of gasoline and light gas oil than atemperature of 1150 F., indicating that further increases would be evenless desirable.

As a further example, consider a decanted oil from catalytic cracking,having the following properties:

The decanted oil of Table V is divided into three samples, Sample 4being fed at one time to the coking reactor, Sample 5 at another time tothe line 3 at 1150 F. and Sample 6 at still another time to the sameline 3 at l100 F., the temperature being controlled by small changes inthe burning and recycle rates of the coke. Yields from the three samplesare shown in Table VII, together with the yields from normal operation,Sample 0, in which there is no addition of any decanted oil.

TABLE VII Fluid Cokz'ng Yields of Samples 4, 5, and 6 Samples NormalOpera- 4 5 6 tion Dry Gas (C2 minus) M s.c.f./d. 27, 000 27,665 33, 60030, 450 Total Propanes, b./d 2,81 ,84 3, 73S 3, 276 Total Butanes, b./d1,974 1,994 2,436 2, 226 Gasoline (39 Rate Di ,d 12,222 12, 317 12, 51612, 558 Light Gas Oil (600 F. at 90% Dist.), b./d 4, 578 4, 723 4, 7034, G20

Heavy Gos Oil (630 F. Plus), b./d 13, B02 18, 297 15, 442 16, 192 Coke,Gross, M lbs/d 3, 046 3, 690 3, 844 753 a carbons by contact with adense uidized bed of heated coke particles in a coking zone and the bedis maintained at coking temperature by circulation of coke particlesfrom said bed to a burning zone wherein a portion thereof is burned toheat the remainder substantially above the temperature of said bed andthus heated colse particles art returned to said bed through anelongated transfer zone,

the method of simultaneously cracking a heavy oil more refractory andmore volatile than said charge oil which comprises introducing only saidmore refractory oil into said transfer zone to travel therethrough incontact with heated coke particles therein, for a distance suflicientthat said more refractory oil is cracked therein at a temperaturesubstantially above that to which said charge oil is subjected. 2. Aprocess as in claim 1 wherein the more refractory oil is a heavy gasoil. i

3. A process as in claim 1 wherein the more refractory oil is a decantoil.

4. A process as in claim l wherein the more refractory oil is a mixtureof a heavy gas oil and a decant oil.

References Cited in the le of this patent UNITED STATES PATENTS2,777,802 Peet lan. 15, 1957 2,868,715 Jahnig et al Jan. 13, 19592,894,897 Post July 14, 1959 2,920,032 Vander Ploeg et al Ian. 5, 1960

1. IN A FLUID COKING PROCESS WHEREIN A HEAVY HYDROCARBON CHARGE OIL ISCRACKED TO LOWER BOILING HYDROCARBONS BY CONTACT WITH A DENSE FLUIDIZEDBED OF HEATED COKE PARTICLES IN A COKING ZONE AND THE BED IS MAINTAINEDAT COKING TEMPERATURE BY CIRCULATION OF COKE PARTICLES FROM SAID BED TOA BURNING ZONE WHEREIN A PORTION THEREOF IS BURNED TO HEAT THE REMAINDERSUBSTANTIALLY ABOVE THE TEMPERATURE OF SAID BED AND THUS HEATED COKEPARTICLES ART RETURNED TO SAID BED THROUGH AN ELONGATED TRANSFER ZONE,THE METHOD OF SIMULTANEOUSLY CRACKING A HEAVY OIL MORE REFRACTORY ANDMORE VOLATILE THAN SAID CHARGE OIL WHICH COMPRISES INTRODUCING ONLY SAIDMORE REFRACTORY OIL INTO SAID TRANSFER ZONE TO TRAVEL THERETHROUGH INCONTACT WITH HEATED COKE PARTICLES THEREIN, FOR A DISTANCE SUFFICIENTTHAT SAID MORE REFRACTORY OIL IS CRACKED THEREIN AT A TEMPERATURESUBSTANTIALLY ABOVE THAT TO WHICH SAID CHARGE OIL IS SUBJECTED.